고체역학 (Beer) — Stress and Strain—Axial Loading: Problem 2.40

2.40 Three steel rods ($E = 200 \text{ GPa}$) support a $36\text{-kN}$ load $P$. Each of the rods $AB$ and $CD$ has a $200\text{-mm}^2$ cross-sectional area, and rod $EF$ has a $625\text{-mm}^2$ cross-sectional area. Neglecting the deformation of bar $BED$, determine (a) the change in length of rod $EF$, (b) the stress in each rod.